The invention relates to electric contact material of the type consisting essentially of a porous matrix of a refractory metal, particularly tungsten or molybdenum, and having its pores impregnated with a metal alloy.
Material of this type is used for making the contacts of heavy-duty vacuum switches relied on to make a high number of switching cycles. Such contacts must meet stringent requirements with respect to burn-off resistance, for example, resistance to burn-off may be required for more than 10.sup.6 switching cycles at the rated current capacity of the switch. Such contacts should have the ability to control interrupt currents of from 2 to 3 kA. A low welding or sticking force between the opening switch contacts is also required, a typical requirement being that the force required for contact separation should be less than 300 newtons for pulse currents of 300 kA, and the interrupt current must be small, for example, less than 5 A.
In addition to the above requirements, for reasons of mechanized production of such vacuum switches, it should be possible to easily solder the contacts to the contact carrying studs or current conducting elements of the switches.
To cope with the foregoing requirements, electric contact material has been made by powder metal techniques in combination of WCu, MoCu or WCuBi; or by metallurgical melting processes, from NiCTe. WCu and MoCu contacts meet the requirements as to burn-off resistance, low interrupt current and solderability, but not the requirement as to low welding force. Contacts of WCuBi provide a low welding force, but according to the present state of the art, are not solderable. NiCTe, on the other hand, has insufficient service life because of excessive burn-off.